This invention relates generally to electric incandescent lamps of the type which provide radiant energy efficiently and more particularly to a structural configuration for the filament light source means employed in this type lamp to improve its operating efficiency.
A wide variety of electric incandescent lamps are already known which employ a refractory metal filament as the light source to provide general illumination. With the original A-line household lamps of this type, a coiled tungsten filament is commonly employed having opposite end turns extending outwardly along the central coil axis and which are physically clamped for support by refractory metal lead-in wires. If the clamping is too tight it can produce broken filaments while too loose clamping can result in erratic electrical contact producing flicker or electromagnetic interference. A further serious problem arises during customary manufacture wherein the lamps is "flashed" to provide a recrystallized grain structure in the assembled filament. A transition zone of uncrystallized refractory metal often occurs at the junction site of clamping which is also recognized to enhance mechanical breakage of the supported filament. It would be understandably desirable to eliminate or minimize all such problems with utilization of a coiled refractory metal filament in an electric incandescent lamp.
Recent development of increasingly more energy efficient electric incandescent lamps places a far greater requirement upon physical location of the refractory metal incandescent filament in the lamp envelope. For example, one known lamp emits selectively in both the infrared and visible spectral regions with such lamp providing studio lighting having a daylight color. A representative structural configuration for said type lamp is disclosed in U.S. Pat. No. 4,588,923, assigned to the assignee of the present invention, and wherein the selective radiant energy distribution from the lamp is achieved with a reflective film deposited on the elongated lamp envelope. As can be noted from the description appearing in said commonly assigned prior art patent, the optical pass-band and the stop-band characteristics selected for said reflective film medium serve to reflect infrared radiation back to the lamp filament. The filament operating efficiency can be increased in this manner for more efficient light output from the lamp since the reflective film is selected so as to still transmit a major portion of the desired visible radiation. The above mentioned patent is specifically incorporated herein by reference, therefore, due to the same reflective film characteristics which can be employed in one embodiment of the present lamp improvement. The doubled ended lamp construction disclosed in said prior art patent is further reported to mechanically and electrically connect an elongated tungsten filament extending substantially the full length of a tubular lamp envelope with lead-in wires joined thereto by known "spudding" techniques. Such joinder of the filament coil to the lead-in wire conductors is customarily provided by inserting one end of a lead-in wire length into the central coil opening and thereafter welding the inserted end to a number of the end coil turns. In doing so, it can be appreciated that the lighted length of the coil filament may vary widely especially due to melting of the lead-in refractory metal which can short circuit a variable number of these end turns. While such method of securing a coiled filament to its lead-in conductors has proven acceptable, as evidenced by current wide scale commercial practice, it still remains difficult to assemble the lead-in conductors into both ends of a filament coil with ease and high reliability. Accordingly, it remains desirable to provide such type filament assembly in a manner enabling more precise determination of the lighted length for the assembled filament coil as well as enabling said light source to be conveniently and accurately positioned within the lamp envelope during lamp manufacture.
It is a principal object of the present invention, therefore, to provide a more reliable coiled filament assembly in an electric incandescent lamp employing an elongated hermetically sealed light transmissive envelope and in a manner producing an improved light source.
It is another important object of the present invention to provide improved filament connection means in such type electric incandescent lamps enabling a coiled refractory filament to be aligned substantially coincident with the longitudinal axis of the lamp envelope in a convenient simple manner.
Still another important object of the present invention is to provide more effective engagement between the filament member and its lead-in conductors which better controls centering of the assembled filament within the lamp envelope.
A still further important object of the present invention is to provide an improved coiled filament assembly in said type electric incandescent lamp enabling still more reliable lamp manufacture, particularly with high speed automated lamp manufacturing equipment.
These and other objects of the present invention will become more apparent upon consideration of the following description for the present invention.